1. Field of the Invention
The present invention relates to a method for cleaning a liquid ejection head.
2. Description of the Related Art
A liquid ejection head that ejects a liquid using a heat generating resistive element used, for example, in an inkjet printer is proposed. This liquid ejection head includes a flow path forming member that forms a flow path of a liquid, such as ink, and a heat generating resistive element. The heat generating resistive element is formed, for example, by an electrothermal converting element. When the heat generating resistive element is made to generate heat, the liquid is heated suddenly and foams in a liquid contact area (i.e., a thermal action portion) located above the heat generating resistive element. Foaming produces pressure with which the liquid is ejected from ejection ports. An image is recorded on a surface of a recording medium, such as a paper sheet, with the liquid. To insulate the heat generating resistive element from the liquid, covering the heat generating resistive element with an insulating layer is proposed. The heat generating resistive element receives the following complex actions: physical actions including impact due to cavitation caused by foaming and deaeration of the liquid, and chemical actions caused by the liquid. Therefore, covering the heat generating resistive element with a coating layer for protection is proposed.
In a liquid ejection head, the following phenomenon may occur: an additive, such as a coloring material included in a liquid, is decomposed when heated at a high temperature, the additive changes into a highly insoluble substance, and the additive is physically absorbed into a layer in contact with the liquid, such as an insulating layer and a coating layer. The physically absorbed object is called “kogation.” When kogation adheres to the protective layer, uneven heat conduction from a thermal action portion to the liquid may occur, foaming may become unstable, and ejection characteristics of the liquid may be adversely affected.
To address this problem, Japanese Patent Laid-Open No. 2008-8364 and Japanese Patent Laid-Open No. 2010-137554 each disclose a configuration in which an electrically connectable upper protective layer (i.e., a coating layer) is disposed in an area including a thermal action portion to form an electrode that provokes electrochemical reaction with a liquid. These Patent Documents disclose removing kogation by eluting a surface of the upper protective layer by the electrochemical reaction.